package/rustc: fix target names for i586 and i686

Commit d69d40c029dc (package/rustc: add support for Tier 1 and Tier 2
platforms) misspelled the config options for i586 and i686.

They are BR2_x86_i586 and BR2_x86_i686, not BR2_i586 or BR2_i686.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Romain Naour <romain.naour@smile.fr>

---
Changes v1 -> v2:
  - in commit log: s/BR2_i386_/BR2_x86_/g  (Baruch)

package/rustc/Config.in.host

@@ -25,7 +25,7 @@ config BR2_PACKAGE_HOST_RUSTC_TARGET_TIER1_PLATFORMS
 	# aarch64-unknown-linux-gnu
 	default y if BR2_aarch64 && BR2_TOOLCHAIN_USES_GLIBC
 	# i686-unknown-linux-gnu
-	default y if (BR2_i686 || BR2_x86_pentiumpro || BR2_X86_CPU_HAS_MMX) && BR2_TOOLCHAIN_USES_GLIBC
+	default y if (BR2_x86_i686 || BR2_x86_pentiumpro || BR2_X86_CPU_HAS_MMX) && BR2_TOOLCHAIN_USES_GLIBC
 	# x86_64-unknown-linux-gnu
 	default y if BR2_x86_64 && BR2_TOOLCHAIN_USES_GLIBC
 
@@ -93,11 +93,11 @@ config BR2_PACKAGE_HOST_RUSTC_TARGET_TIER2_PLATFORMS
 	# userspace
 	default y if BR2_arm && BR2_ARM_CPU_ARMV8A && BR2_ARM_EABIHF && BR2_TOOLCHAIN_USES_MUSL
 	# i586-unknown-linux-gnu
-	default y if BR2_i586 && BR2_TOOLCHAIN_USES_GLIBC
+	default y if BR2_x86_i586 && BR2_TOOLCHAIN_USES_GLIBC
 	# i586-unknown-linux-musl
-	default y if BR2_i586 && BR2_TOOLCHAIN_USES_MUSL
+	default y if BR2_x86_i586 && BR2_TOOLCHAIN_USES_MUSL
 	# i686-unknown-linux-musl
-	default y if (BR2_i686 || BR2_x86_pentiumpro || BR2_X86_CPU_HAS_MMX) && BR2_TOOLCHAIN_USES_MUSL
+	default y if (BR2_x86_i686 || BR2_x86_pentiumpro || BR2_X86_CPU_HAS_MMX) && BR2_TOOLCHAIN_USES_MUSL
 	# mips-unknown-linux-musl
 	default y if BR2_mips && BR2_TOOLCHAIN_USES_MUSL && !BR2_MIPS_CPU_MIPS32R6
 	# mips64-unknown-linux-muslabi64