toolchain/Config.in: correct BR2_TOOLCHAIN_HEADERS_AT_LEAST for 5.17

Missed from commit 2b134f9549d ({toolchain, linux-headers}: add support for
5.17.x headers).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 484b50507f31e90a3f955698ad10e7aad6f91b37)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

toolchain/Config.in

@@ -580,6 +580,7 @@ config BR2_TOOLCHAIN_HEADERS_LATEST
 # stops affecting a value on the first matching default.
 config BR2_TOOLCHAIN_HEADERS_AT_LEAST
 	string
+	default "5.17" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_17
 	default "5.16" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_16
 	default "5.15" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_15
 	default "5.14" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_14