perf tools: Version incorrect with some versions of grep

perf tools: Version incorrect with some versions of grep

Some versions of grep don't treat '\s' properly. When building perf on such
systems and using a kernel tarball the perf version is unable to be determined
from the main kernel Makefile and the user is left with a version of '..'.
Replacing the use of '\s' with '[[:space:]]', which should work in all grep
versions, gives a usable version number.

Reported-by: Tapan Dhimant <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Tapan Dhimant <[email protected]>
Cc: [email protected]
Cc: [email protected]
LKML-Reference: <1300241800[email protected]>
Signed-off-by: Josh Hunt <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>