regulator: core: allow long device tree supply regulator property names

The length 32 buffer in of_get_regulator() limits the maximum
possible supply name to 24 characters (32 - 1 [null terminator]
- 7 [strlen("-supply")]).  This causes problems for device
nodes with longer supply property names.

Increase the size of the buffer to remove this artificial
restriction.

Change-Id: Ic28ee290dcd7411ba8325a2b42c12173958a11d8
Signed-off-by: David Collins <collinsd@codeaurora.org>