devtools: fix letter case check in commit title

devtools: fix letter case check in commit title

The prefix (before the colon) of the title is lowercase.
The check of uppercase/lowercase in the commit title
was supposed to apply after the colon,
but some greps were not limited to the exact word.
So in the case of "test/dma: add basic dmadev instance tests",
the lowercase word "dmadev" was wrongly suggested to be uppercase.

The words of the dictionary must be filtered as whole word
with the grep option -w.

Fixes: d448efa259e9 ("devtools: export dictionary for commit title check")
Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>