checkpatch: Eliminate false positive in case of space before square bracket in a definition

Now, macro definition such as "#define abc(x) [x] = y" should pass
without an error.

Signed-off-by: Leonid Bloch <leonid@daynix.com>
Message-Id: <1446112118-12376-3-git-send-email-leonid@daynix.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
