x86/cpu/amd: Remove unnecessary parentheses

Clang warns when multiple pairs of parentheses are used for a single
conditional statement.

arch/x86/kernel/cpu/amd.c:925:14: warning: equality comparison with
extraneous parentheses [-Wparentheses-equality]
        if ((c->x86 == 6)) {
             ~~~~~~~^~~~
arch/x86/kernel/cpu/amd.c:925:14: note: remove extraneous parentheses
around the comparison to silence this warning
        if ((c->x86 == 6)) {
            ~       ^   ~
arch/x86/kernel/cpu/amd.c:925:14: note: use '=' to turn this equality
comparison into an assignment
        if ((c->x86 == 6)) {
                    ^~
                    =
1 warning generated.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181002224511.14929-1-natechancellor@gmail.com
Link: https://github.com/ClangBuiltLinux/linux/issues/187


Signed-off-by: Ingo Molnar <mingo@kernel.org>