meson: adjust ssl dep name

Adjust the ssl dependency name to `ssl_dep` to fit meson conventions.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1673bec30c1594d8c8d528322760449744424e36
diff --git a/meson.build b/meson.build
index b00229d..a93cdd2 100644
--- a/meson.build
+++ b/meson.build
@@ -57,7 +57,7 @@
 
 deps = [cereal_dep, pdi_dep, phosphor_logging_dep, sdbusplus_dep]
 
-ssl = dependency('openssl')
+ssl_dep = dependency('openssl')
 
 systemd = dependency('systemd')
 systemd_system_unit_dir = systemd.get_variable('systemd_system_unit_dir')