fastchg: change fast charge to override the high current GPIO, not the USB cable mode

I wrote this patch, and built it, but I'm not able to test it on my device -- kernels that I build from this source seem to crash my device along the lines of:

```
[  216.738372] Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
[  216.738494] Modules linked in:
[  216.738616] CPU: 0    Not tainted  (3.0.73-tinykernel-4.0.1-gf56f287-dirty #2)
[  216.738739] PC is at twofish_decrypt+0x3e0/0xc58
[  216.738800] LR is at crypto_cbc_decrypt+0x140/0x180
```

I suspect some issue with my toolchain; either way, the patch should be sound, though.  Give it a spin?