wctdm24xxp: Use framecount and not jiffies when looking for battery present.

The logic to check for battery lost and battery present were using different
time bases. One was using jiffies and the other was using framecount. This could
result in cases where a battery goes into alarm but never comes out.

This fixes a regression introduced in 2.6.0 with commit (r10169 "wctdm24xxp: Use
interval for debouncing FXO battery." 874b76bd223313e22a773725be63c1b4b64cb274).

Signed-off-by: Shaun Ruffell <sruffell@digium.com>