boot/arm-trusted-firmware/Config.in: fix 'platform' typo

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 2e3c0ab1b7bbe8bb5a5abb493fc81e166593ac8f)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/arm-trusted-firmware/Config.in

@@ -77,7 +77,7 @@ endif
 config BR2_TARGET_ARM_TRUSTED_FIRMWARE_PLATFORM
 	string "ATF platform"
 	help
-	  Target plaform to build for.
+	  Target platform to build for.
 
 config BR2_TARGET_ARM_TRUSTED_FIRMWARE_TARGET_BOARD
 	string "ATF target board"