SamsungExynos4RIL: fix signal strength

Doesn't work with Gingerbread radios!

Since ICS, the modem sends the signal strength in the first 8 bits
and the number of bars as from bit 9.
For old radios the first 8 bits are always 99.

Change-Id: I67b31baf18cbce2dfa7e6f8b096caaae74cd7cd8