serial-dmm: Use dummy info struct for rs9lcd parser

The rs9lcd parser, which is used for the RadioShack 22-812 does not use its
*info parameter, and therefore did not have a rs9lcd_info struct declared.

With recent re-factoring of the receive data callbacks, it became necessary to
pass a struct pointer. This made the RECV_DATA macro look like:

- RECV_DATA(RADIOSHACK_22_812, metex14)

giving the wrong impression that the RadioShack 22-182 uses the
metex14 protocol, which is not the case.

Create a dummy rs9lcd_info struct, and correctly identify the parser
as rs9lcd in the RECV_DATA macro:

+ RECV_DATA(RADIOSHACK_22_812, rs9lcd)

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>

hardware/serial-dmm/protocol.c

@@ -201,4 +201,4 @@ RECV_DATA(METEX_M3640D, metex14)
 RECV_DATA(PEAKTECH_4370, metex14)
 RECV_DATA(PCE_PCE_DM32, fs9721)
 RECV_DATA(RADIOSHACK_22_168, metex14)
-RECV_DATA(RADIOSHACK_22_812, metex14)
+RECV_DATA(RADIOSHACK_22_812, rs9lcd)

libsigrok-internal.h

@@ -210,6 +210,9 @@ SR_PRIV int sr_metex14_parse(const uint8_t *buf, float *floatval,
 
 #define RS9LCD_PACKET_SIZE 9
 
+/* Dummy info struct. The parser does not use it. */
+struct rs9lcd_info {};
+
 SR_PRIV gboolean sr_rs9lcd_packet_valid(const uint8_t *buf);
 SR_PRIV int sr_rs9lcd_parse(const uint8_t *buf, float *floatval,
 			    struct sr_datafeed_analog *analog, void *info);