libdvbv5: Rename internally-defined poll function as dvb_poll

libdvbv5: Rename internally-defined poll function as dvb_poll

poll() is the name of a glibc function. Rename it as dvb_poll().

That should likely fix a Coverity warning:

278     		do {
>>>     CID 1233564:  Out-of-bounds access  (ARRAY_VS_SINGLETON)
>>>     Passing "&parms->p" to function "poll" which uses it as an array. This might corrupt or misinterpret adjacent memory locations. [Note: The source code implementation of the function has been overridden by a builtin model.]
279     			available = poll(&parms->p, dmx_fd, timeout);
280     		} while (available < 0 && errno == EOVERFLOW);

Also, as this function is static, use the private struct directly.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>