checkpatch: Fix commit log check for a filename

Checkpatch fails to identify the filename with a comma (usually
dt-binding files), and issues the following warning, for example:
WARNING: Possible unwrapped commit description
(prefer a maximum 75 chars per line)
bindings/qcom,foo.yaml | 27 +++++++++++++++++++++++++

Hence, include a comma (,) in the regular expression where it
checks for file delta changes while scanning through the commit
log.

Change-Id: I07000722c1990c7171769e222c5f9aefa1d87ae6
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>