perf alias: Remove trailing newline when reading sysfs files

Remove a trailing newline when reading sysfs file contents such as
/sys/devices/cpum_cf/events/TX_NC_TEND.  This shows when verbose option
-v is used.

Output before:

  tx_nc_tend -> 'cpum_cf'/'event=0x008d
  '/

Output after:

  tx_nc_tend -> 'cpum_cf'/'event=0x8d'/

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20180615101105.47047-1-tmricht@linux.ibm.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>