main: Address strncat() overflow warning
```
FAILED: debug-trigger.p/main.c.o
ccache cc -Idebug-trigger.p -I. -I.. -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -Werror -std=gnu18 -O0 -g -MD -MQ debug-trigger.p/main.c.o -MF debug-trigger.p/main.c.o.d -o debug-trigger.p/main.c.o -c ../main.c
../main.c: In function ‘main’:
../main.c:549:17: error: ‘strncat’ specified bound 4096 equals destination size [-Werror=stringop-overflow=]
549 | strncat(devnode, devid, sizeof(devnode));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
```
Change-Id: Id9abfb900ad7601acd595febf00eb92c5a56d3af
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/main.c b/main.c
index 8bfec4d..cf2e2de 100644
--- a/main.c
+++ b/main.c
@@ -546,7 +546,7 @@
devid = basename(devpath);
strncpy(devnode, "/dev/", sizeof(devnode));
- strncat(devnode, devid, sizeof(devnode));
+ strncat(devnode, devid, sizeof(devnode) - strlen("/dev/"));
devnode[PATH_MAX - 1] = '\0';
if ((sourcefd = open(devnode, O_RDONLY)) == -1)