msm: adsprpc: Fix memory out of bounds error

At present the kernel memory allocation does
not allocate memmory for character "_" in debugfs
file format i.e. <file>_<pid>.

This patch fixes memory out of bound error by
allocating memory to the under-score("_")character.

Change-Id: I9cc11b5231ba3654588eadf7a7adca68aff35684
Signed-off-by: Mohammed Nayeem Ur Rahman <mohara@codeaurora.org>