Fix braced initializer list (NFC)

After r270617 I am getting an error when building:

projects/compiler-rt/lib/profile/InstrProfilingFile.c:33:36:
error: missing field 'PidChars' initializer
[-Werror,-Wmissing-field-initializers]
lprofFilename lprofCurFilename = {0};
                                   ^

Fix the aggregate initializer.

llvm-svn: 270697