rename osim_file_find_* to osim_file_desc_find_*

they return an osim_file_desc, and not an osim_file, so fix the naming
diff --git a/include/osmocom/sim/sim.h b/include/osmocom/sim/sim.h
index e818a65..d7c4242 100644
--- a/include/osmocom/sim/sim.h
+++ b/include/osmocom/sim/sim.h
@@ -240,13 +240,13 @@
 
 
 struct osim_file_desc *
-osim_file_find_name(struct osim_file_desc *parent, const char *name);
+osim_file_desc_find_name(struct osim_file_desc *parent, const char *name);
 
 struct osim_file_desc *
-osim_file_find_fid(struct osim_file_desc *parent, uint16_t fid);
+osim_file_desc_find_fid(struct osim_file_desc *parent, uint16_t fid);
 
 struct osim_file_desc *
-osim_file_find_sfid(struct osim_file_desc *parent, uint8_t sfid);
+osim_file_desc_find_sfid(struct osim_file_desc *parent, uint8_t sfid);
 
 /* STATUS WORDS */