rust: bindgen: -Wimplicit-fallthrough=% does not use quotes anymore

Mainline commit cd8c917 ('Makefile: Do not quote value for
CONFIG_CC_IMPLICIT_FALLTHROUGH') fixes the added quotes in the flags,
thus we do not need the special case anymore.

This reverts commit 56aa8af ('rust: bindgen: fix filtering of
`-Wimplicit-fallthrough=%`').

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/Makefile

@@ -202,12 +202,9 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
 	-Wno-packed-not-aligned -Wno-format-truncation -Wno-format-overflow \
 	-Wno-stringop-truncation -Wno-unused-but-set-variable \
 	-Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized \
-	-Werror=designated-init -Wno-zero-length-bounds \
+	-Werror=designated-init -Wno-zero-length-bounds -Wimplicit-fallthrough=% \
 	-Wno-alloc-size-larger-than --param=% --param asan-%
 
-# We need to keep the quotes for this one -- it comes from a `Kconfig`
-bindgen_skip_c_flags += "-Wimplicit-fallthrough=%"
-
 # PowerPC
 bindgen_skip_c_flags += -mtraceback=no -mno-pointers-to-nested-functions \
 	-mno-string -mno-strict-align